With the development of increasingly mechanized systems for the mining, preparation and transportation of coal has come an increase in the quantity of fine coal particles produced. Such fine coal particles, commonly known as coal dust, are often lost during coal handling. Both wind and flowing water readily carry coal dust away. Coal losses due to wind and water are often substantial and add directly to the costs of coal as a fuel.
Ironically, once coal has been transported to an industrial site for usage, it often must be pulverized before burning. Pulverized coal forms fine particles similar to coal dust in many respects. Because of the high surface to volume ratios of coal particles, the coal itself has greater contact with atmospheric oxygen when in particulate form. This physical characteristic of coal particles explains, at least in part, the desirability of feeding industrial furnaces with pulverized coal rather than larger coal fragments. In other words, fine coal particles burn more efficiently than larger coal fragments.
Prior art in the field of this invention has been primarily directed toward the alleviation of coal dust losses by capturing the coal dust before its dispersal in the environment and then converting it into a stable form. In U.S. Pat. No. 3,655,350, issued to Utley in 1972, coal pellets with certain desirable characteristics were produced. These pellets contained coal dust, coal tar pitch and less than ten percent water. The pellets produced were reasonably stable to crushing and impact forces as well as resistant to water induced degradation. Drying the pellets in a fluid bed dryer for forty seconds at seven hundred and fifty degrees did not adversely affect pellet structure nor cause substantial losses of physical stability. Pellets using bentonite clay as a binder were found to have little resistance to destruction by water.
In U.S. Pat. No. 3,377,146, issued to von Stroh in 1968, a coal pellet containing coal dust and lignosulfonate binder is produced. The binder is a water soluble lignin derivative and serves to facilitate pellet formation. The resultant pellets were found to withstand temperatures of fourteen hundred degrees without loss of hardness.
In U.S. Pat. No. 4,025,596, issued to Parks, et al. in 1977, a method of pelletizing fine particles using a non-water soluble latex polymer and a hydrophilic agglutinant is taught. In some cases polyethylene glycol was used as an agglutinant along with a latex binder and fine coal particles. Pellets produced were dried, as example 1 indicates, at 200.degree. F. for two hours.
As indicated by reports on agglomeration (Chemical Engineering, October 1951, 161-65 and Chemical Engineering, Dec. 4, 1967, 147-69) and by the common knowledge of practicioners of the art, the most frequently used coal particle binders in the past have been hydrophobic substances such as petroleum asphalt and coal tar or sometimes bentonite clays. Such pellets, although stable, are prone to burn inefficiently as compared to pulverized coal and also to sometimes produce noxious gases and become gummy when subjected to heat. In some cases excessive ash is produced. Such pellets, for efficient industrial combustion, must be first mechanically pulverized back to fine coal particles.
It is an object of the present invention to produce a stable coal pellet from fine coal particles which might otherwise be lost during coal preparation and transportation.
Yet another object of this invention is to produce a coal pellet which will burst into combustible coal dust particles upon subjection to heat such as during injection into a furnace.
Other objects and advantages of this invention will be evident from the following description of the preferred embodiment and accompanying tabular data.